A microprocessor is an electronic device capable of performing the processing and control functions for computing devices such as desktop computers, laptop computers, server computers, cell phones, laser printers, and so on. Typically, a microprocessor comprises a small plastic or ceramic package that contains and protects a small piece of semiconductor material that includes a complex integrated circuit. Leads connected to the integrated circuit are attached to pins that protrude from the package allowing the integrated circuit to be connected to other electronic devices and circuits. Microprocessors are usually plugged into or otherwise attached to a circuit board containing other electronic devices.
While a microprocessor integrated circuit typically includes only one computing unit, i.e., one processor, it is possible to include multiple processors in a microprocessor integrated circuit. The multiple processors, which are often referred to as “cores,” are included in the same piece of semiconductor material and connected to the microprocessor package pins. Having multiple cores increases the computing power of the microprocessor. For example, a microprocessor with four cores can provide almost the same amount of computing power as four single-core microprocessors. Harnessing the increased computing power that multiple-core microprocessors provide allows computing functions that previously required multiple computing devices to be performed with fewer computing devices.
For example, a server implemented across 32 traditional computing devices, i.e., a 32-way server, may be implemented by eight microprocessors, each having four cores. Taking the concept one step further, if each individual core is eight times more powerful than one of the 32 computing devices, a 32-way server may be implemented by one microprocessor with four cores. Reducing the number of microprocessors reduces the cost of the server, the amount of energy required to power the server, and the amount of maintenance the server requires.
The advantages of using multiple-core microprocessors is driving a trend toward “server consolidation.” Server consolidation is the process of taking multiple servers, possibly each providing a different service, and providing all of the services on one physical device, e.g., a four-core processor. While reducing costs, energy, and maintenance, consolidating servers has the effect of putting all of one's eggs into one basket. This puts a greater burden of reliability on the one physical device. If a server is implemented on many separate computing devices and a computing device fails, usually there are other computing devices that are able to take over for the failed computing device. The process of having one computing device take over for a failing computing device is referred to as “failover.” Techniques have been developed for traditional server configurations to perform failover in a controlled and orderly fashion to ensure that no data is lost and no ongoing processes are interrupted during the transition from the failing computing device to the replacement computing device.
In order to create multiple-core microprocessor servers that are as robust and reliable as single-core microprocessor servers, similar techniques are required.